How to add user to a Group in Linux
Add user to a Group
usermod - modify user accountA user does not belong to a specific group could cause application problem.
To check a user's existing group:
$ id user_name
To add an existing user to a group:
For example, to add user ec2-user to docker group:
$ sudo usermod -aG docker ec2-user
You need to logout and login to see the effect.
Be careful not to use
It will change the user's primary group, instead of just adding to the group.